如何在Java中正确覆盖toString（）？

Question

听起来有点愚蠢，但我需要toString()方法的帮助，这非常令人讨厌。 我尝试在网上查找，因为toString是它正在搞砸了“并没有找到Kid构造函数＃2”，即使它在那里，我甚至会做其他事情并且它不起作用。 好的，这就是我的代码：

import java.util.*; 
   class Kid {  
      String name; 
      double height; 
      GregorianCalendar bDay; 

      public Kid () { 
         this.name = "HEAD";
         this.height = 1; 
         this.bDay = new GregorianCalendar(1111,1,1); 
      } 

      public Kid (String n, double h, String date) {
      // method that toString() can't find somehow
         StringTokenizer st = new StringTokenizer(date, "/", true);
         n = this.name;
         h = this.height;
      } 

      public String toString() { 
         return Kid(this.name, this.height, this.bDay);
      } 
   } //end class 

好的，所以上面的toString（我知道，我的第三个参数是关闭的，应该是一个String）是关闭的。如果我硬编码第三件事的价值它会变得混乱，并说它找不到这个（上面）。那么我怎样才能得到日期并将其分解？

调用此类的课程在

之下

class Driver {   
   public static void main (String[] args) {   
      Kid kid1 = new Kid("Lexie", 2.6, "11/5/2009");   
      System.out.println(kid1.toString());
   } //end main method 
} //end class  

我尝试过研究多个构造函数，但实际上并没有帮助。 我尝试研究toString()方法，并尝试使用我之前创建的以前的toString()方法逻辑，但这是全新的，因此它从未起作用。

帮助？

Answer 1

toString应该返回String。

public String toString() { 
    return "Name: '" + this.name + "', Height: '" + this.height + "', Birthday: '" + this.bDay + "'";
} 

我建议您使用IDE的功能来生成toString方法。不要手工编码。

例如，如果只需右键单击源代码并选择Source > Generate toString

，Eclipse就可以这样做

Answer 2

Java toString（）方法

如果要将任何对象表示为字符串，则toString（）方法就会出现。

toString（）方法返回对象的字符串表示形式。

如果打印任何对象，java编译器会在内部调用对象上的toString（）方法。所以重写toString（）方法，返回所需的输出，它可以是对象的状态等取决于你的实现。

Java toString（）方法的优点

通过重写Object类的toString（）方法，我们可以返回对象的值，因此我们不需要编写太多代码。

没有toString（）方法的输出

class Student{  
 int id;  
 String name;  
 String address;  

 Student(int id, String name, String address){  
 this.id=id;  
 this.name=name;  
 this.address=address;  
 }  

 public static void main(String args[]){  
   Student s1=new Student(100,”Joe”,”success”);  
   Student s2=new Student(50,”Jeff”,”fail”);  

   System.out.println(s1);//compiler writes here s1.toString()  
   System.out.println(s2);//compiler writes here s2.toString()  
 }  
}  

Output:Student@2kaa9dc
       Student@4bbc148

您可以在上面的示例＃1中看到。打印s1和s2打印对象的Hashcode值，但我想打印这些对象的值。由于java编译器内部调用toString（）方法，因此重写此方法将返回指定的值。让我们通过下面给出的例子来理解它：

Example#2

Output with overriding toString() method

class Student{  
 int id;  
 String name;  
 String address;  

 Student(int id, String name, String address){  
 this.id=id;  
 this.name=name;  
 this.address=address;  
 }  

//overriding the toString() method  
public String toString(){ 
  return id+" "+name+" "+address;  
 }  
 public static void main(String args[]){  
   Student s1=new Student(100,”Joe”,”success”);  
   Student s2=new Student(50,”Jeff”,”fail”);  

   System.out.println(s1);//compiler writes here s1.toString()  
   System.out.println(s2);//compiler writes here s2.toString()  
 }  
} 

Output:100 Joe success
       50 Jeff fail

请注意，toString（）主要与Java中的多态性概念有关。 在Eclipse中，尝试单击toString（）并右键单击它。然后，单击Open Declaration并查看Superclass toString（）的来源。

Answer 3

您可以在toString（）中创建新对象。 使用

return "Name = " + this.name +" height= " + this.height;

而不是

return Kid(this.name, this.height, this.bDay);

您可以根据需要更改返回字符串。还有其他方法来存储日期而不是calander。

Answer 4

您无法将构造函数称为普通方法，只能使用new调用它来创建新对象：

Kid newKid = new Kid(this.name, this.height, this.bDay);

但是从你的toString（）方法构造一个新对象并不是你想要做的。

Answer 5

以下代码是一个示例。基于相同的问题而不是使用基于IDE的转换，是否有更快的实现方式，以便将来发生更改时，我们不需要反复修改值？

@Override
    public String toString() {
        return "ContractDTO{" +
                "contractId='" + contractId + '\'' +
                ", contractTemplateId='" + contractTemplateId + '\'' +
                '}';
    }

Answer 6

实际上你需要返回这样的东西，因为toString必须返回一个字符串

public String toString() {
 return "Name :" + this.name + "whatever :" + this.whatever + "";
}

你实际上在构造函数中做了一些错误，你将用户设置的变量设置为名称，而你需要做相反的事情。 你应该做什么

n = this.name

你应该做什么

this.name = n

希望这有助于谢谢

Answer 7

我们甚至可以这样编写，方法是在类中创建一个新的String对象，并在构造函数中为它指定我们想要的东西，并在被覆盖的toString方法中返回

public class Student{  
 int id;  
 String name;  
 String address;  
 String details;
 Student(int id, String name, String address){  
 this.id=id;  
 this.name=name;  
 this.address=address;  
 this.details=id+"  "+name+"  "+address;  
 }  

//overriding the toString() method  
public String toString(){ 
  return details;  
 }  
 public static void main(String args[]){  
   Student s1=new Student(100,"Joe","success");  
   Student s2=new Student(50,"Jeff","fail");  

   System.out.println(s1);//compiler writes here s1.toString()  
   System.out.println(s2);//compiler writes here s2.toString()  
 }  
}

Answer 8

如果您对单元测试感兴趣，则可以声明一个公共的“ ToStringTemplate”，然后可以对toString进行单元测试。即使您不对其进行单元测试，我也认为它“更干净”并使用String.format。

extensions [ view2.5d ]

globals [ max-sheep ]  ; don't let sheep population grow too large
; Sheep and wolves are both breeds of turtle.
breed [ sheep a-sheep ]  ; sheep is its own plural, so we use "a-sheep" as the singular.
breed [ wolves wolf ]
turtles-own [ energy ]       ; both wolves and sheep have energy
patches-own [ countdown ]

to setup
  clear-all

  ifelse netlogo-web? [set max-sheep 10000] [set max-sheep 30000]

  ; Check model-version switch
  ; if we're not modeling grass, then the sheep don't need to eat to survive
  ; otherwise the grass's state of growth and growing logic need to be set up
  ifelse model-version = "sheep-wolves-grass" [
    ask patches [
      set pcolor one-of [ green brown ]
      ifelse pcolor = green
        [ set countdown grass-regrowth-time ]
      [ set countdown random grass-regrowth-time ] ; initialize grass regrowth clocks randomly for brown patches
    ]
  ]
  [
    ask patches [ set pcolor green ]
  ]

  create-sheep initial-number-sheep  ; create the sheep, then initialize their variables
  [
    set shape  "sheep"
    set color white
    set size 1.5  ; easier to see
    set label-color blue - 2
    set energy random (2 * sheep-gain-from-food)
    setxy random-xcor random-ycor
  ]

  create-wolves initial-number-wolves  ; create the wolves, then initialize their variables
  [
    set shape "wolf"
    set color black
    set size 2  ; easier to see
    set energy random (2 * wolf-gain-from-food)
    setxy random-xcor random-ycor
  ]
  display-labels
  reset-ticks

  view2.5d:turtle-view "wsp" turtles [ t -> [energy] of t ]

end

to go
  ; stop the simulation of no wolves or sheep
  if not any? turtles [ stop ]
  ; stop the model if there are no wolves and the number of sheep gets very large
  if not any? wolves and count sheep > max-sheep [ user-message "The sheep have inherited the earth" stop ]
  ask sheep [
    move
    if model-version = "sheep-wolves-grass" [ ; in this version, sheep eat grass, grass grows and it costs sheep energy to move
      set energy energy - 1  ; deduct energy for sheep only if running sheep-wolf-grass model version
      eat-grass  ; sheep eat grass only if running sheep-wolf-grass model version
      death ; sheep die from starvation only if running sheep-wolf-grass model version
    ]
    reproduce-sheep  ; sheep reproduce at random rate governed by slider
  ]
  ask wolves [
    move
    set energy energy - 1  ; wolves lose energy as they move
    eat-sheep ; wolves eat a sheep on their patch
    death ; wolves die if our of energy
    reproduce-wolves ; wolves reproduce at random rate governed by slider
  ]
  if model-version = "sheep-wolves-grass" [ ask patches [ grow-grass ] ]
  ; set grass count patches with [pcolor = green]
  tick
  display-labels

  view2.5d:update-turtle-view "wsp" turtles

end

to move  ; turtle procedure
  rt random 50
  lt random 50
  fd 1
end

to eat-grass  ; sheep procedure
  ; sheep eat grass, turn the patch brown
  if pcolor = green [
    set pcolor brown
    set energy energy + sheep-gain-from-food  ; sheep gain energy by eating
  ]
end

to reproduce-sheep  ; sheep procedure
  if random-float 100 < sheep-reproduce [  ; throw "dice" to see if you will reproduce
    set energy (energy / 2)                ; divide energy between parent and offspring
    hatch 1 [ rt random-float 360 fd 1 ]   ; hatch an offspring and move it forward 1 step
  ]
end

to reproduce-wolves  ; wolf procedure
  if random-float 100 < wolf-reproduce [  ; throw "dice" to see if you will reproduce
    set energy (energy / 2)               ; divide energy between parent and offspring
    hatch 1 [ rt random-float 360 fd 1 ]  ; hatch an offspring and move it forward 1 step
  ]
end

to eat-sheep  ; wolf procedure
  let prey one-of sheep-here                    ; grab a random sheep
  if prey != nobody  [                          ; did we get one?  if so,
    ask prey [ die ]                            ; kill it, and...
    set energy energy + wolf-gain-from-food     ; get energy from eating
  ]
end

to death  ; turtle procedure (i.e. both wolf nd sheep procedure)
  ; when energy dips below zero, die
  if energy < 0 [ die ]
end

to grow-grass  ; patch procedure
  ; countdown on brown patches: if reach 0, grow some grass
  if pcolor = brown [
    ifelse countdown <= 0
      [ set pcolor green
        set countdown grass-regrowth-time ]
      [ set countdown countdown - 1 ]
  ]
end

to-report grass
  ifelse model-version = "sheep-wolves-grass" [
    report patches with [pcolor = green]
  ]
  [ report 0 ]
end


to display-labels
  ask turtles [ set label "" ]
  if show-energy? [
    ask wolves [ set label round energy ]
    if model-version = "sheep-wolves-grass" [ ask sheep [ set label round energy ] ]
  ]
end



; Copyright 1997 Uri Wilensky.
; See Info tab for full copyright and license.

现在，您可以通过创建Kid，设置属性并在ToStringTemplate上进行自己的string.format并进行比较来进行单元测试。

使ToStringTemplate静态最终意味着真相的“一个版本”，而不是在单元测试中拥有模板的“副本”。

Answer 9

总有一种简便的方法：右键单击> 生成> toString（）>选择所需的模板。

Answer 10

正如其他人解释的那样，persist()并不是实例化您的课程的地方。相反，toString方法旨在构建一个表示您的类的实例的值的字符串，至少报告存储在该对象中的数据的最重要字段。在大多数情况下，toString用于调试和日志记录，而不用于您的业务逻辑。

toString

从Java 8和更高版本开始，实现StringJoiner的最现代方法将使用StringJoiner类。

类似这样的东西：

toString

  

Person [name = Alice | phone = 555.867.5309]

Answer 11

我认为最好的方法是使用Google gson库：

        @Override
public String toString() {
    return new GsonBuilder().setPrettyPrinting().create().toJson(this);
}

或apache commons lang反射方式

Answer 12

1. 如果您使用记事本： 然后

   public String toString(){
   
    return ""; ---now here you can use variables which you have created for your class
   
   }
   

2. 如果您使用的是Eclipse IDE，则 按

   -alt +shift +s 
   

   -单击覆盖toString方法，在这里您将获得选择要选择的变量类型的选项。

Answer 13

简洁明了的方法是使用Lombok批注。它具有@ToString批注，它将生成toString()方法的实现。默认情况下，它将按顺序打印您的班级名称以及每个字段，并以逗号分隔。 您可以通过将参数传递给注释来轻松自定义输出，例如：

@ToString(of = {"name", "lastName"})

相当于纯Java：

public String toString() {
        return "Person(name=" + this.name + ", lastName=" + this.experienceInYears + ")";
    }

Answer 14

如果仅使用toString()来调试DTO，则可以使用以下内容自动生成可读的输出：

import com.fasterxml.jackson.databind.ObjectMapper;
...
public String toString() {
    try { return new ObjectMapper().writeValueAsString(this); }
    catch (Exception e) { return "{ObjectMapper failed}"; }
}

---

但是，如果DTO可能包含PII（不应在日志中捕获），则这不适用于生产部署。